Soft contact lenses are usually disinfected either by short-term heating at a temperature over 80.degree. in an isotonic sodium chloride solution or by treatment at room temperature with such solution containing disinfecting chemical agents.
Disinfecting by heating is more advantageous from several points of view. A more reliable result is reached, and at the same time the risk of accumulating contamination, which might harm the eyes, in the lens material is avoided. This is especially important since disinfection of the lenses must normally be carried out once every 24 hours.
The heating devices for contact lenses, which are on the market today, operate according to one of the following basic principles.
A reservoir, in which the lenses are kept in isotonic sodium chloride solution, is lowered into a water-bath which is then heated to over 80.degree. C. When the water in the water-bath has evaporated, the temperature rises rapidly, whereupon a thermoswitch turns off the current at a predetermined temperature. When the apparatus has cooled, the lens receptacle may be taken out and the lenses worn.
According to another procedure the lens receptacle, which in principle may be of the same design as the one in the above "water-bath method", is placed in a device where the receptacle is heated by direct transport of heat from a heated surface in the apparatus. Here, too, high temperatures in the heat source are used so that the lenses in an isotonic sodium chloride solution are heated to over 80.degree. C. By means of a thermoswitch, the temperature in the lens receptacle is adjusted so as to prevent boiling. After cooling, the receptacle and the lenses may be taken out.
The lens receptacle of above-mentioned design may be a jar with a lid or a closed box in which the lens is fastened in a holder designed especially for this purpose, the design being such that while being heated the lens is in contact with the sodium chloride solution. The lens receptacle may be so designed that both lenses share a volume of liquid or so that each lens has its own volume of liquid.